Background: The incidence of coexisting papillary thyroid cancer (PTC) and Hashimoto's thyroiditis (HT) is increasing. The impact of HT on PTC prognosis and its possible mechanism remains controversial. Interleukin-17A (IL-17A) has been reported to participate in the pathogenesis of multiple autoimmune diseases and cancers. The aim of this study is to investigate the role of IL-17A in PTC with coexistent HT and evaluate the changes in tumor antigenicity.
Methods: Expression of IL-17A and major histocompatibility complex (MHC) class I molecules were compared on PTC tissue samples with or without HT. PTC cell lines K1 and TPC-1 were stimulated with IL-17A and analyzed for MHC class I expression afterwards. Cluster of differentiation (CD) 8+T cell activation, production of Interleukin-2 (IL-2) and Interferon-gamma (IFN-γ) as well as the programmed death-1 (PD-1) expression on lymphocytes were assessed by coculture of donor peripheral blood lymphocytes (PBLs) with IL-17A pretreated PTC cells.
Results: Elevated IL-17A and MHC class I expression were observed in PTC tissue samples with coexistent HT. Stimulation of PTC cells with IL-17A effectively increased MHC class I expression in vitro. Coculture of PBLs with IL-17A pretreated PTC cells resulted in enhanced T cell activation (%CD25+ of CD3+T cells) and increased IL-2 production along with decreased IFN-γ secretion and PD-1 expression of the lymphocytes.
Conclusions: Papillary thyroid cancer with coexisting Hashimoto's thyroiditis presents elevated MHC class I expression, which may be the result of IL-17A secretion. T cell activation is enhanced in vitro by IL-17A and may provide future utility in PTC immunotherapy.
Keywords: Hashimoto’s thyroiditis; Immune escape; Interleukin-17A; MHC class I molecule; PD-1/PD-L1; Papillary thyroid cancer.